Cacodominus

The Cacodominus was the name given to an extremely powerful alien-cyborg Psyker who was behind The Howling in M34. The Cacodomius' powers were such that it was able to exert complete control over an area of 1,300 planetary systems. Eventually, it was slain by the Black Templars, but the resulting backlash distorted the signal of the Astronomican and burnt out billions of Astropaths across the Imperium. The resulting anarchy from the events resulted in millions of ships being lost and entire Sub-Sectors descending into barbarism.[1]